Optical recorder

ABSTRACT

Non-impact printing or recording apparatus adapted for use with a digital computer. The apparatus is characterized by the employment of an optical character generator and timing system therefor capable of printing information on a moving photoresponsive medium. The apparatus is further characterized by the provision of a field mask disposed intermediate a lens system and the photosensitive medium which field mask prevents projection of more than one character from a column of characters.

United States Patent Rees [54] OPTICAL RECORDER [.72] Inventor: James D. Rees, Pittsford, N.Y.

[73] Assignee: Xerox Corporation, Stamford,

Conn. [22] Filed: Dec. 28, 1970 i [21] Appl. No.: 101,701

[52] US. Cl ..95/4.5 R, 178/330, 355/3 [51] Int. Cl. ..B41b 15/06, B4lb 17/34 [58] Field of Search ..95/4.5; l78/6.7 R, 15, 30;

[56] References Cited UNITED STATES PATENTS 2,944,147 7/1960 Bolton ..95/4.5 R 3,249,028 5/1966 Higonnet et al; ..95/4.5 R

2,726,940 12/1955 ,Buhler ..95/4.5R

[451 Dec. 12,1972

2,736,770 2/1956 McNaney, ..9s/4.s R 5,252,592 5/1966 Ward.; ....9s/4.5 R 3,254,579

6/1966 Higonnet et al. ..95/4.5

. Primary Examiner-Robert P. Greiner Attorney-James J. Ralahate, John E. Beck and Benjamin B. Sklar [57] ABSTRACT Non-impact printing or recording apparatus adapted for use with a digital computer. The apparatus is characterized by the employment of an optical character generator and timing system therefor capable of printing information on a moving photoresponsive medium. The apparatus is further characterized by the provision of a field mask disposed intermediate a lens system and the photosensitive medium which .field mask prevents projection of more than one character from a column of characters.

10 Claims, 14 Drawing Figures PATENTED DEC 12 I972 SHEET 1 OF 8 INVENTOR. JAMES 0. REES PATENTED on: 12 1912 3. 705. 543

sum 2 or a PATENTED are 12 I972 SHEEI 5 BF 8 PATENTEU DEC 1 2 I972 SHEEI 6 0F 8 aux PATENTEU DEC 1 2 I972 SHEET 7 [IF 8 PATENTED DEC 12 I972 SHEET 8 [IF 8 TIME T O START OF LINE (START OF FIRST QUADRANT) T 5! l l ssc.

(END OF FIRST QUADRANT) (START OF SECOND QUADRANT) g l I T SEC. 1

(END OF SECOND QUADRANT) 2| T T n sec.

(START OF THIRD QUADRANT) I T 9 0/ sEc.

(END OF THIRD QUADRANT) T SEC.

(START OF FOURTH QUADRANT) T 9 sec.

(END OF FOURTH QUADRANT) COLUMN 2 3 4 V ONE CHARACTER SPACE(S) 2&1? Z

' n Z END OF LINE proximity thereto produces uneven Moreover, such devices are bulky and complicated.

I OPTICAL RECORDER I BACKGROUND OFTHE INVENTION 'This invention relates, in general, to high speed printing and, more particularly, to optical character printers compatible with digital computer output.

Earlier attempts atcompu'ter output printing of the type herein contemplated led to the development of shadowgraph printing wherein illumination from a flash lamp passes through transparent characters to thereby form a shadow image or images on a recording medi- Exposure in such a system-is determined by the solid angle subtended by the flash lamp are at the character mask. Hence, exposure increases as the arc size is inresults in the employment of a very small flash lamp,

requiring a very small xenon fill pressure which varies widely in the manufacturing process, resulting in variations in light output from lamp to lamp. Furthermore, the wall area to electrode volume ratio is small, consequently, lamp blacking caused by electrode sputtering limits the life of the lamp to about flashes at 8 millijoules per flash. Still further such lamps are limited to 1:1 printing.

In solving the' foregoing problem one may utilize small unconfined, commercially available, are lamps which have a life greater than 10 flashes at 8 millijoules per flash. A simple lamp cover enclosing each lamp can be provided as a partial diffuse integrating cavity. To carry the light from the lamp to the recording medium, with shadowgraphing or optical imaging, an incoherent'fiber bundle could be provided. Such an arrangement exhibits a very low efficiency (i.e., about percent) which requires a very high energy input which substantially shortens the life of the lamp.

Characteristically incoherent fiber bundles when'illuminated with a small light source placed in close illumination.

For example, fora computer printout format of 132 columns, the printer needs 132 flash lamps and related circuitry plus 132 fiber bundles all of which have to be packed into a character mask structure.

Accordingly, the general object of the invention is to provide new and improved printing apparatus.

It is a more particular object of this invention to provide new and improved printing apparatus wherein computer outputs of 132 characters per line can be printed on an 1 Hitch wide copy sheet.

'Another object of this invention is to provide a new and improved optical system for'an optical printer.

Still another object of this invention is to provide a new and improved character mask for use in an optical printer. 1

Yet another objectof this invention is to provide a new and improved printing apparatus utilizing optical imaging on a rotating photoconductive drum.

Still another object of this invention is to provide a field mask for an optical printer which field masks prevents projection of more than one character from a column of characters on a charactermask.

' BRIEF DESCRIPTION OF THE INVENTION Briefly, the above-cited objects are accomplished by the provision of a transparent character drum having staggered columns or sets of characters extending about the circumference thereof. Inthe preferred embodiment'there are 132 such columns divided into groups of four such that each group of four columns ex tends around the entire circumference of the character drum. In this manner there are 33 groups of four columns each.

In groups are spaced apart along the longitudinal axis of the drum a distance at least equal to the distance across one group. This permits the projection of properly spaced, enlarged images, onto a rotating photoconductive drum.

A strip prism arrangement or equivalent mirror system cooperates with 33 commercially available flash lamps and suitable condenser lenses to transmit illumination from the lamps through-the character drum images in the direction of a strip lens structure serving to form the images on a rotating photoconductive drum. The individual elements of the prism arrangement are disposed relative to one another so as to intercept light travelling in three different directions and transmit the light therefrom in one direction so that in conjunction with suitable timing means associated with the character drum, an entire line can be printed for each revolution of the character drum.

The timing means comprises a plurality of slits on the character drum which are so arranged with respect to the characters on the character drum that all the characters to be contained in a line on the photoconductive drum can be registered in that line even though the variouscharacters forming the line pass the light from the prisms at different points in time and even though the photoconductive drum is continuously rotating.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a schematic view of printing apparatus representing the invention;

FIG. 2 is a schematic perspective view of an optical character mask and optical projection system forming a part of the apparatus illustrated in FIG. 1;

FIG. 3 is a block diagram depicting the cycle of operation for generating optical characters by means of the mask and projection system of FIG. 2;

FIG. 4 is an expanded view as viewed from the outside of the character mask illustrated in FIG. 2;

FIG. 5 is an expanded view as viewed from the outside of a character mask utilized for the purpose of providing a better understanding of the invention;

FIGS. 6 and 7 are schematic perspective views of the character drum of FIG. 5 illustrating the projection of the characters thereof onto a photoconductive surface;

FIGS. 8-10 are similar to FIGS. 5-7, but illustrate a timing slit arrangement and its effect on the projection of characters onto the photoconductive surface;

.muun s...-

FIG. 11 is an enlarged schematic perspective view of the optical system forming a part of the invention;

FIG. 12 is a schematic perspective view illustrating a field mark forming a part of the projection system hereof;

FIG. 13 is a time sequential representation of the characters on the character mask at the time of their projection onto the photoconductive surface as viewed through a stationary field mask; and

FIG. 14 is an enlarged plan view of the field mask and character mask illustrating the simultaneous projection of three consecutive characters of the character mask.

DETAILED DESCRIPTION OF THE INVENTION General As shown schematically in FIG. 1, the automatic xerographic recording apparatus comprises a xerographic plate 20 including a photoconductive layer or light-receiving surface on a conductive backing and formed in the shape of a drum, which is mounted on a shaft journalled in a frame to rotate in the direction indicated by the arrow to cause the drum surface sequentially to pass a plurality of xerographic processing stations.

For the purpose of the present disclosure, the several xerographic processing stations in the path of movement of the drum surface may be described functionally, as follows:

A charging station, at which a uniform electrostatic charge is deposited on the photoconductive layer of the xerographic drum;

An exposure station, at which a light or radiation pattern of information to be recorded is projected onto the drum surface to dissipate the drum charge in the exposed areas thereof and thereby form latent electrostatic images of the information to be recorded;

A developing station, at which xerographic developing material including toner particles having electrostatic charges opposite to that of the electrostatic latent images are cascaded over the drum surface, whereby the toner particles adhere to the electrostatic latent images to form xerographic powdered images in the configuration of the information being recorded.

A transfer station, at which the xerographic powder images are electrostatically transferred from the drum surface to a transfer material or support surface; and,

A drum cleaning and discharge station, at which the drum surface is brushed to remove residual toner particles remaining thereon after image transfer, and at which the drum surface is exposed to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining thereon.

The charging station is preferably located, as indicated by reference character A. As shown, the charging arrangement includes a corona charging device 21 which includesa corona discharge array one or more corona discharge electrodes that extend transversely across the drum surface and are energized from a high potential source and are substantially closed within a shielding member.

Next subsequent thereto in the path of motion of the xerographic drum is an exposure station 8. A flash expose optical projection system is provided to project an image onto the surface of the photoconductive drum.

The optical projection system comprises a stationary lens and prism structure generally indicated 23 comprising a plurality of prisms arranged to reflect light, emanating from a plurality of directions, in one direction through a character mask in the shape of a drum 24. The lamps associated with the prisms and character mask are adapted to be flashed in accordance with output from a digital computer, in such a manner as toenable printing of an entire line for each revolution of the character drum.

Adjacent to the exposure station is a developing station C in which there is positioned a developer apparatus 30 including a casing or housing having a lower or sump portion for accumulating developer material. A bucket type conveyor is used to carry the developing material to the upper part of the developer housing where it is cascaded over a hopper chute onto the xerographic drum to effect development. A toner dispenser 35 is used to accurately meter toner to the developing material as toner particles are consumed during the developing operation.

Positioned next and adjacent to the developing station is the image transfer station D which includes a sheet feeding arrangement adapted to feed sheets of support material, such as paper or the like, successively to the xerographic drum in coordination with the presentation of the developed image on the drum surface at the transfer station.

The sheet feeding mechanism includes a sheet feed device 40 adapted by means of vacuum feeders to feed the top sheet of a stack of sheets on a tray 41, to rollers 42 cooperating with the belts of paper transport 44 for advancing the sheet sufficiently to be held by paper transport 44 which in turn, conveys the sheet to a sheet registration device 45 positioned adjacent to the xerographic drum. The sheet registration device arrests and aligns each individual sheet of material and then in timed relation to the movement of the xerographic drum, advances the sheet material into contact with the xerographic drum in registration with a previously formed xerographic powder image on the drum.

The transfer of the xerographic powder image from the drum surface to the sheets of support material is effected by means of a corona transferdevice 51 that is located at or immediately after the line of contact between the support material and the rotating drum. In operation, the electrostatic field created by the corona transfer device is effective to tack the support material electrostatically to the drum surface, whereby the support material moves synchronously with the drum while in contact therewith. Simultaneously with the tacking action, the electrostatic field is effective to attract the toner particles comprising the xerographic powder image from the drum surface and cause them to adhere electrostatically to the surface of the support material.

Immediately subsequent to the image transfer station there is positioned a stripping apparatus or paper pickoff mechanism 52 for removing the sheets of support material from the drum surface. This device, includes a plurality-of small diameter orifices supplied with pressurized aeriform fluid by a suitable pulsator or other device. The pulsator is adapted to force jets of pressurized aeriform fluid through the outlet orifices into contact with the surface of the xerographic drum slightly in advance of the sheet of support material to strip the leading edge of the sheet from the drum surface and to direct it onto an endless conveyor 55 whereby the sheet material is carried to a fixing device 60. At the fixing device, the transferred xerographic powder image on the sheet of support material is permanently fixed or fused thereto as by the application of heat. After fusing, the paper is discharged from the'apparatus at a suitable point for collection externally of the apparatus by means of the conveyor65. In the embodiment shown, the papers are discharged from conveyor 65 into a receiving tray 61.

The next and final station in the device is a drum cleaning station E, having positioned therein a corona preclean device 66, a drum cleaning device 70 adapted to remove any powder remaining on the xerographic drum after transfer by means of a rotating brush 71, and'a discharge lamp LMP-l adapted to flood the xerographic drum with light to cause dissipation of any residual electrical charge remaining on the xerographic drum.

. For collecting powder particles removed from. the

xerographic drum by the brush 71, there is provided a dust hood 73 that is formed to encompass approximately two-thirds of the brush area. To ensure thorough cleaning of the brush, a flicking bar 74 is secured to the interior of the dust hood adjacent the edge of the outlet duct 75 of the dust hood and in interfering relation with the ends of the brush bristles whereby dust particles may be dislodged therefrom.

For removing dust particles from the brush and dust hood, an exhaust duct 76 is arranged to cover the outlet of the dust hood, the exhaust duct being connected at its other end to the wall of a filter box 77 attached to powder particles removed from the drum by the brush as the air flows through the dust hood. Powder particles are separated from the air as it flows through the filter bag so that only clean air reaches the motor unit.

Suitable drive means are provided to drive the drums and sheet feed mechanism at predetermined speeds relative to each other, and to effect operation of the bucket-type conveyor and toner dispenser mechanism and the other operating mechanisms.

The character mask or drum 24 forms a part of an optical projection system comprising the lens and prism structure 23, to be discussed in detail hereinafter, and a plurality of flash lamps 100.

The flash lamps 100 are fiashable in accordance with information derived from a computer, the illumination therefrom being directed by means of the lens and prism structure 23 through characters of the character mask 24 which characters may be either opaque or transparent. The characters so formed produce latent electrostatic images of alphanumeric characters on the photoconductive plate 20.

Each of the character spaces occupied by a character on the xerographic plate is associated with a transparent slit or aperture 102, the slits being disposed about the circumference of the drum. A slit sensor 104 disposed adjacent the outer surface of the drum intercepts a light from alight source 106 each time a slit 102 passes between the sensor and the light source. Pulses generated by the sensor 104 are utilized, as will be discussed hereinafter, to effect firing of the lamps 100.

The block diagram of FIG. 3 illustrates, in general, the cycle of operation for firing of the flash lamps in accordance with the output from a computer 108 which is utilized as a buffer storage device containing sufficient data to print a complete page of 66 lines. A model DDP 516 computer manufactured by Honeywell Corporation has been satisfactorily employed to demonstrate the operation of the printer.

Initially only a portion of the data contained in the buffer device 108 is written into a memory device 110 which may comprise a pair of FT 40 fast access memory cards having a capacity of 16 two-character words at 16 bits per word. Such cards are manufactured by Xerox Data Systems. Writing into memory is accomplished by means of a process control shift register 112 driven by a 5 MHz clock. The shift register also controls the reading of the data into a comparator 114 which may comprise suitable logic components, for example, AND gates (not shown) for deriving outputs when positive comparisons are made. The other input to the AND gates may be derived from a counter 116.

The counter 116 is preset to a code representing the first character on the character drum 24. Accordingly, when the first or initial portion of data is read into the comparator 110 it is compared to the code representing the aforementioned first character or in other words the preset value of the counter. Each successive character on the character drum is represented by a code in the counter on incrementing thereof. This incrementing of the counter is accomplished by virtue of the pulses from the slit sensor 104. It can be seen that the code representing the second character on the drum will be represented by the preset value of the counter plus 1.

When the code in the comparator 114 is the same as the code from the memory 110, a latch 1 18, which may comprise a flip-flop (not shown) is set. Pulses from the sensor 104 are ANDed with the outputs from the latches to thereby actuate lamp firing circuits 120.

In accordance with the objects of the present invention, the character mask or drum 24, as illustrated in FIG. 4, comprises columns 124 of characters disposed on the periphery thereof in groups of four columns. In the preferred embodiment of the invention 33 such groups of four columns each, are disposed along the longitudinal axis of the drum, each group being spaced from adjacent groups by at least a distance equal to the width of one group of columns. The circumferential extent of one group of columns is such that each column of a group occupies a different quadrant of the drum. This produces a staggered arrangement of the columns or character sets which permit utilization of one flash lamp for each group of four columns. If the columns were not staggered but were disposed in a side by side array a lamp would be required for each column.

' Since the columns 124 are staggered, each flash lamp is fired four times for each revolution of the character drum. Accordingly, during one revolution, data corresponding to the first column of each group is put into the comparator 11,4 and compared against the code in the counter l 16. Since one fourth of the data in the buffer is handled at one time, this quantity of data may be thought of as one quadrant of data.

For each column of information from the memory 110 that contains an A, a corresponding latch 118 is set. Subsequent thereto, when the slit 102 associated with the character space for the A is sensed by the sensor 104, the lamp firing circuits 120 corresponding to the latches previously set are triggered. Simultaneously, the pulse from the sensor 104 increments the counter 116 by one. The code for the letter B is now in the comparator and is subsequently compared to the first quadrant of data from the buffer. Each character of the first column is compared in the foregoing manner to the first quadrant of data.

At the end of each column 124 adjacent the last character space of that column there is provided a transparent slit 125 which effects pulsing of a photodetector 132, the pulse from which conditions the register 112 for writing the second quadrant of data from the buffer into memory with subsequent reading from memory into the comparator. The second quadrant of data is read into the comparator, as before, for each character of the second column, each character of the second column being placed one at a time into the comparator as above. The sequence of operation for the third and fourth quadrants of data from the buffer is the same as described above.

As can be seen from FIG. 4, the slits 102 do not occupy the same relative position with respect to their associated character spaces. In other words the slit associated with the first letter of any first column is disposed adjacent the trailing edge of the first character space assuming that the character mask of FIG. 4 is moving upwardly past a flash exposure station. The slit associated with the last character of the group is adjacent the leading edge of that character space.

The purpose of the specific arrangement of the slits 102 will be better understood by first considering the operation of a character mask on which the slits are spaced the same, relative to each character space i.e., adjacent the trailing edge of the space. To this end, reference may be had to FIGS. 5, 6 and 7 wherein there is disclosed an expanded view as viewed from the outside (FIG. of a character mask or drum 140 having a plurality of columns 142 of characters disposed thereon in a side by side relationship. The character drum is adapted for rotation in the counterclockwise direction while a photosensitive insulating plate 144 optically aligned therewith is adapted for rotation in the clockwise direction.

Each column 142 of characters, herein illustrated as the capital letters of the alphabet, represents a character set which extends over the entire circumference of the character drum. In the present embodiment it is desired to print a complete line of characters on the photoconductive plate 144 which line comprises one character from each column of the character drum. Accordingly, flash lamps, not shown, associated, one with each column, will flash once for each revolution of the character drum. Meanwhile, the photoconductive plate rotates the equivalent of one character space. A column of timing slits, one for each character of a column, generally indicated by reference character 146, is sensed to thereby cooperate with an output from a computer to cause flashing of the lamps in accordance with the characters to be recorded. In this particular embodiment each timing slit occupies the same position relative to the character space associated with a particulate character, as all other slits. In other words, each timing slit is in line with the trailing edge of the character space occupied by the character associated therewith.

As shown in FIG. 6, the character A from the first column from the left, is projected onto the photoconductive plate in the position shown, which position lies below a stationary reference line 148 used herein for illustration purposes only. Assuming that the Z of the fourth column is to be projected onto the plate, it will be seen that because the photoconductive plate has moved clockwise a full line or character space the'Z is projected onto the drum, not'on the same line space as the A but one line space below. This is due to the fact that with such a timing slit arrangement all characters are projected below the reference line and by the time the Z moves through the optical axis the line space on the drum containing the A has moved above the reference line.

In order to obviate this problem a plurality of differently spaced timing slits 150, one for each character set is provided adjacent the right edge of a character drum 152. (See FIGS. 8-10). These slits or indicia may be apertures in the character drum or transparent windows in an opaque mask. Either of the foregoing may be employed, the essential requirement being the capability of passing light from the light source 106 to the light sensor 104 which may be a photodiode. The sensor and light source are in line with the optical axis extending between the two drums.

The slits or windows, as shown in FIG. 8 are arranged relative to columns 154 of character such that the one associated with the A is substantially in line with the trailing edge of the character space occupied by the A and the one associated with the character space occupied by the Z is substantially in line with the leading edge of the character space occupied by the Z. The slits or windows intermediate the ones associated with the A and Z are incrementally progressed such that the one associated with the M is substantially in line with the middle of the character space occupied thereby. It can be seen from FIG. 8 that when the slit associated with the A (first column from left) passes the light sensor 104, the A is projected onto a plate 156 in an area that lies below an reference line 158. From FIG. 10, it can be seen that when the slit associated with the Z (fourth column from left) passes the light sensor, the Z on the drum is in a position so as to be projected onto the plate in a position above the reference line, which position due to the clockwise rotation of the plate is in line with the position of the A.

In the preferred embodiment of the character mask, columns 124, as shown in FIG. 4, are placed on a character drum 24 in groups of four, the drum being sufficiently long (i. e. 9.9 inches) to place 33 such groups thereon with a space between groups greater than the distance across the columns in any one group. As shown the columns of each group are staggered such that the columns in one group, beginning with the first character of the first column or set from the left, and ending with the last character of the fourth column or set, extend substantially the circumference of the drum. As in the case of the embodiment of FIGS. -7, it is intended that a line comprising a character from each column or set be printed for each revolution of the drum.

Since the columns of one group, in the embodiment shown, occupy only one fourth of the circumferential extent or one quadrant of the drum, four characters from each group must be projected onto the same line of a photoconductor plate for each revolution of the character drum 24. Expressed another way, a character from each column "in a group must be projected for every one-quarter revolution of the character drum. During this quarter revolution the line space on the photoconductive plate moves one fourth its total distance. This means that for the characters for any two adjacent columns to be projected onto the same line space of the plate, the timing slits 102 associated with those two characters should be approximately one fourth the total distance between the first and last timing slits of one group. To this end the character drum 24 has, as shown in FIG. 4, the first one of timing slits 102 in line with the trailing edge of the character space associated with the A and the last timing slit of fourth column of the first group in line with the leading edge of the character space associated with the last Z in that group. It will be seen upon further examination that the timing slit associated with the character space associated with the Z of second column of the same group occupies a space in line with the middle of the Z.

While the number of columns in each group is illustrated as being four, this need not be the case. Any number of convenient columns may be employed depending on the particular application and the end result desired.

By referring to FIGS. 1 and 4 and bearing in mind the discussion relative to FIGS. 5-7, it can be seen that for each group of columns, an A, by way of example, can be projected onto and along the same line on the plate 20 for each column position of the character drum. Projection of characters commences when the timing slit associated with the first A of the first column is sensed by the light sensor. At this time the first A is projected onto the plate which then rotates clockwise one fourth of a line space while the character drum rotates approximately .a quarter of a revolution. Now the timing slit for the second A is sensed by the light sensor. It will be apparent that the differential spacing of these two timing slits relative to their respective As causes the second A to be projected onto the photoconductive plate a distance one fourth of a line space higher than the preceding A thereby placing the second A on exactly the same line on the plate as the first A. With respect to the third A, it will be seen that its timing slit will have the effect of causing the third A to be projected one half of a line space higher on the plate thereby placing it on the same line with the first two characters. Simultaneously, the projection of other first, second and third A's of the other groups has taken place along the same line of the plate.

The slit sensor 104 is disposed, for sake of convenience 90 from the optical axis. However, it may occupy any location relative to the mask.

The lens and prism structure 23, as best shown in FIGS. 1 and 11, comprises a prism structure 160 which may be fabricated as a single piece or may be assembled from individual prism elements 162 and blocks 163. A plurality of strip condensers 164 comprising condenser elements 166 cooperate with condenser elements 167 molded on the strip prism to collect the illumination from the lamps 100 for transmission to the prism elements 162.

The lamps 100 of which there are thirty-three in the preferred embodiment are arranged in three rows to form an arc of approximately 270 about the top, bottom and rear sides of the strip prism structure 160. The rows of lamps are offset to each other, the top row being offset to the right side of the back row, as viewed from the left in FIG. 11, while the bottom row is offset to the left side of the top row. The amount of offsetting in each of the foregoing cases is equal to four column widths at the photoreceptor 20. The collected light from each lamp in the top and bottom rows is reflected by the strip prism structure in the forward direction toward the character mask 24. While the orientation of the top and bottom lamps are illustrated as being approximately 90" from the back row any practical angle orientation is considered within the scope of this invention.

The light output from they back row of the lamps travels straight through the blocks 163 which are disposed intermediate a pair of prism elements 162.

The illuminated characters are magnified approximately three times and are projected onto the photoconductive drum 20 by means of a strip lens 170. One element (i. e. one individual lens) of the strip lens covers or images four characters on the drum. As shown, these reduced size character columns are grouped on the character drum leaving the aforementioned spaces between groups, hence, the character groups are readily baffled by means of a baffle struccomprises an opaque portion 182 and a plurality of clear portions or windows 185, one such clear portion for each character. Each group of four windows forms a stepped pattern which in combination with the slits 102 serves a purpose which will be discussed hereinafter.

FIG. 13 illustrates the time sequence of the characters A and Z on the outside of the character mask 181 at the time of their projection. By way of example, these two characters are intended to represent the first and last characters of each column or character set. One group of four columns is taken as representative of the entire character mask. It follows from a study of FIG. 13 that the stationary field mask illustrated in FIGS. 12 and 14 in no way inhibits the projection of any of the characters shown in FIG. 13. It is noted that the vertical height of the transparent portions 184 is 25 percent larger than one character space.

FIG. 14 illustrates that if the characters within a character set or column are separated by one quarter of a character space, and the mask 180 is employed, one and only one character from a particular column is projected at a given time. The stepped portions are repetitive for each group of columns.

While the incorporation of the field mask 180 has been shown to allow for reduction of the vertical inter character spacing on the character mark 181 from one blank character space to one fourth of one blank character space, other reductions are possible. For example, is instead of four columns in each group on the character mask there were five columns in each group the character spacing would be reduced to one fifth of a character space. The inter character spacing is directly related to the numberof columns extending about the circumference of the character mask. It can be appreciated that where there is only one column extending about the circumference of the mask, it is necessary to have a complete character space between adjacent characters but where the number of columns of characters extending about the circumference is greater than one the character space can be reduced by a fraction equal to one over the number of columns.

Accordingly, the photoreceptor drum 20 is rotated at a speed such that it moves l/c X s during l/c revolutions of the character mask, where c is equal to the number of columns in a group and s is equal to the height of one character onto the plate 20.

One ramification of being able to reduce the vertical inter character spacing is to allow the diameter of the character drum to be increased to place sufficient characters on the drum to allow the printing of two lines of information per revolution of the drum. The optical system and actual character size remain the same. The resulting decrease of required angular velocity of the character drum reduces the tensile stress on the drum. Another possible modification of the character drum in view of the reduced character spacing would be to allow the character drum diameter and angular velocity to remain the same while increasing the size of the characters on the characterdrum and hence reduce the required optical magnification of the characters. Also, the resulting system has advantageous tolerancing effects as will be appreciated by those skilled in the art. What is claimed is: 1. Apparatus for recording alphanumeric characters, said apparatus comprising:

an endless member having staggered columns of transparent characters extending about the circumference thereof, said columns being in groups of at least two columns which groups extend transversely of said endless member, each of said characters occupying a character space substantially equal to the height of a character and being spaced from adjacent characters less than one character space;

first optical means for projecting, in one direction, light emanating from a plurality of directions, said optical means being disposed within said endless member,

a plurality of rows of spaced-apart flash lamps, one

for each group of columns, said flash lamps being disposed in rows of equally spaced lamps which rows are offset one from the other and disposed in an are extending about said first optical means;

second optical means for focusing the illumination passing through said endless member at focal point;

light responsive recording structure positioned at said focal point for receiving focused images of alphanumeric characters;

means for rotating said endless member at a uniform speed;

means for selectively flashing said lamps in accordance with information to be recorded;

means for moving said light responsive recording structure in synchronism with said endless member, and

a field mask for preventing more than one character from any one column from being focused on said light responsive recording structure, said field mask being disposed between said optical means and said light responsive recording structure.

2. Apparatus according to claim 1 wherein, said field masks comprises opaque portions and groups of transparent portions, said transparent portions being equal in size and being sequentially offset in the direction of movement of said recording structure a distance equal to He X s where c is equal to the number of columns in one group and s is equal to the height of a character space.

3. Apparatus according to claim 2 wherein, said means for moving said light responsive recording structure comprises drive means for moving said light responsive recording structure at a speed such that it moves l/c X s during a He revolution of the endless member, where c is equal to the number of columns in one group and s is equal to the height of one character on the light responsive recording structure.

4. Apparatus according to claim 3 wherein, said light responsive recording structure comprises an electrostatic charge-retentive surface and said apparatus further comprises:

means for placing a uniform charge on said surface which is dissipated in accordance with images focused thereon to thereby form an electrostatic latent image, and

means for developing said latent image in order to render it visible.

5. Apparatus for recording alphanumeric characters,

said apparatus comprising:

a cylindrical member having staggered columns of transparent characters extending about the circumference thereof, said columns being disposed in a plurality of groups containing at least two columns, each of said characters occupying a character space substantially equal to the height of a character and being spaced from adjacent characters less than one character space;

means for selectively producing illumination along a predetermined line relative to said cylindrical member and in accordance with information to be recorded;

means for projecting illumination through said cylindrical member and focusing character images on a light responsive medium;

means for rotating said cylindrical member at a uniform speed;

means for moving said light responsive member in synchronism with said cylindrical member; and

a field mask for preventing more than one character from any one column from being focused on said light responsive medium, said field mask being disposed intermediate said cylindrical member and said light responsive member.

6. Apparatus according to claim wherein, said field mask comprises an opaque portion and a plurality of transparent portions, said transparent portions being equal in size and forming a stepped pattern whereby they are offset from each other a distance equal to 1/0 X s where c is equal to the number of columns in said at least one group and s is equal to the height of a character on said light responsive medium.

7. Apparatus according to claim 6 wherein, said means for moving said light responsive medium comprises drive means for movement thereof at a speed such that it moves a distance equal to He X s during a 1/0 revolution of said endless member.

8. Alphanumeric character generating apparatus, said apparatus comprising:

a cylindrical member having staggered columns of transparent characters extending about the circumference thereof, said columns being disposed in a plurality of groups containing at least two columns, each of said characters occupying a character space substantially equal to the height of a character and being spaced from adjacent characters less than one character space;

means for selectively producing illumination in accordance with information to be recorded;

means for projecting illumination through said cylindrical member along a predetermined line relative to said cylindrical member and focusing character images on a light responsive medium;

means for rotating said cylindrical member at a uniform speed;

means for moving said light responsive member in synchronism with said cylindrical member; and

a field mask for preventing more than one character from any one column from being focused on said light responsive member, said field mask being disposed intermediate said endless member and said light responsive member.

9. Apparatus according to claim 8 wherein, said field mask comprises an opaque portion in a plurality of transparent portions, said transparent portions being equal in size and forming a stepped pattern whereby they are offset from each other a distance equal to 1/0 X s where c is equal to the number of columns in said at least one group and s is equal to the height of a character on said light responsive medium.

10. Apparatus according to claim 9 wherein, said means for moving said light responsive member comprises drive means for movement thereof at a speed such that it moves a distance equal to 1/0 X s during a 1/0 revolution of said endless member.

Alain Al 

1. Apparatus for recording alphanumeric characters, said apparatus comprising: an endless member having staggered columns of transparent characters extending about the circumference thereof, said columns being in groups of at least two columns which groups extend transversely of said endless member, each of said characters occupying a character space substantially equal to the height of a character and being spaced from adjacent characters less than one character space; first optical means for projecting, in one direction, light emanating from a plurality of directions, said optical means being disposed within said endless member, a plurality of rows of spaced-apart flash lamps, one for each group of columns, said flash lamps being disposed in rows of equally spaced lamps which rows are offset one from the other and disposed in an arc extending about said first optical means; second optical means for focusing the illumination passing through said endless member at focal point; light responsive recording structure positioned at said focal point for receiving focused images of alphanumeric characters; means for rotating said endless member at a uniform speed; means for selectively flashing said lamps in accordance with information to be recorded; means for moving said light responsive recording structure in synchronism with said endless member, and a field mask for preventing more than one character from any one column from being focused on said light responsive recording structure, said field mask being disposed between said optical means and said light responsive recording structure.
 2. Apparatus according to claim 1 wherein, said field masks comprises opaque portions and groups of transparent portions, said transparent portions being equal in size and being sequentially offset in the direction of movement of said recording structure a distance equal to 1/c X s where c is equal to the number of columns in one group and s is equal to the height of a character space.
 3. Apparatus according to claim 2 wherein, said means for moving said light responsive recording structure comprises drive means for moving said light responsive recording structure at a speed such that it moves 1/c X s during a 1/c revolution of the endless member, where c is equal to the number of columns in one group and s is equal to the height of one character on the light responsive recording structure.
 4. Apparatus according to claim 3 wherein, said light responsive recording structure comprises an electrostatic charge-retentive surface and said apparatus further comprises: means for placing a uniform charge on said surface which is dissipated in accordance with images focused thereon to thereby form an electrostatic latent image, and means for developing said latent image in order to render it visible.
 5. Apparatus for recording alphanumerIc characters, said apparatus comprising: a cylindrical member having staggered columns of transparent characters extending about the circumference thereof, said columns being disposed in a plurality of groups containing at least two columns, each of said characters occupying a character space substantially equal to the height of a character and being spaced from adjacent characters less than one character space; means for selectively producing illumination along a predetermined line relative to said cylindrical member and in accordance with information to be recorded; means for projecting illumination through said cylindrical member and focusing character images on a light responsive medium; means for rotating said cylindrical member at a uniform speed; means for moving said light responsive member in synchronism with said cylindrical member; and a field mask for preventing more than one character from any one column from being focused on said light responsive medium, said field mask being disposed intermediate said cylindrical member and said light responsive member.
 6. Apparatus according to claim 5 wherein, said field mask comprises an opaque portion and a plurality of transparent portions, said transparent portions being equal in size and forming a stepped pattern whereby they are offset from each other a distance equal to 1/c X s where c is equal to the number of columns in said at least one group and s is equal to the height of a character on said light responsive medium.
 7. Apparatus according to claim 6 wherein, said means for moving said light responsive medium comprises drive means for movement thereof at a speed such that it moves a distance equal to 1/c X s during a 1/c revolution of said endless member.
 8. Alphanumeric character generating apparatus, said apparatus comprising: a cylindrical member having staggered columns of transparent characters extending about the circumference thereof, said columns being disposed in a plurality of groups containing at least two columns, each of said characters occupying a character space substantially equal to the height of a character and being spaced from adjacent characters less than one character space; means for selectively producing illumination in accordance with information to be recorded; means for projecting illumination through said cylindrical member along a predetermined line relative to said cylindrical member and focusing character images on a light responsive medium; means for rotating said cylindrical member at a uniform speed; means for moving said light responsive member in synchronism with said cylindrical member; and a field mask for preventing more than one character from any one column from being focused on said light responsive member, said field mask being disposed intermediate said endless member and said light responsive member.
 9. Apparatus according to claim 8 wherein, said field mask comprises an opaque portion in a plurality of transparent portions, said transparent portions being equal in size and forming a stepped pattern whereby they are offset from each other a distance equal to 1/c X s where c is equal to the number of columns in said at least one group and s is equal to the height of a character on said light responsive medium.
 10. Apparatus according to claim 9 wherein, said means for moving said light responsive member comprises drive means for movement thereof at a speed such that it moves a distance equal to 1/c X s during a 1/c revolution of said endless member. 